Method for the separation of alpha-methyl naphthalene from beta-methyl naphthalene by azeotropic distillation



Jan 3, 1952 J. FELDMAN ETAL 2,581,398

METHOD FOR THE SEPARATION OF 1X-METHYL NAPHTHALENE FROM l5 -METHYLNAPHTHALENE BY AZEOTROPIC DISTILLATION INVENTORS Julian Feldman MiltonOrchin ATTORNEY Jan- 8, 1952 J. FELDMAN ETAL 2,581,398

METHOD FOR TEE SEPARATION OE cx-METEYL NAPETHALENE FROM E5-METHYLNAPHTEALENE BY AzEOTRoPIc OTSTTELATION 2 SHEETS-SHEET 2 Filed Aug. 28.1951 E29. LmEotcm M O mm2 2 E29. wEotcm EEEEO En `5:52am o maotomuwrcucoo M. .um

wLmEow. o mts-z Patented Jan. 8, 1952 METHOD FOR THE SEPARATION OFa-METHYL NAPHTHALENE FROM -METHYL NAPHTHALEN E BY AZEO- TROPICDISTILLATION Julian Feldman and Milton Orchin, Pittsburgh, Pa.,assignors to the United States of America as represented by theSecretary of the Interior Original application February 9, 1950, SerialNo. 143,288. Divided and this application August 28, 1951, Serial No.244,084

(Granted under the act of March 3, 1883, as

5 Claims.

amended April 30, 1928; 370 O. G. 757) The invention herein describedand claimed may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof royalties thereon or therefor.

This application is a division of application Serial No. 143,288, filedFebruary 9, 1950, for Method for the Separation of a-Methyl Naphthalenefrom -Methyl Naphthalene by Azeotropic Distillation by Julian Feldmanand Milton Orchin.

This invention relates to a method for separating dicultly separableisomerc organic compounds and is particularly concerned with a methodfor separating amethyl naphthalene from -methyl naphthalene by a processinvolving azeotropic distillation.

Since isomerc compounds have the same molecular weight. virtually thesame chemical structure, and usually have boiling points which are onlya few degrees apart, the separation of isomers from one another isusually a diicult matter. Direct fractional distillation of the isomermixture, and conventional methods of azeotropic distillation usually areimpractical. In the case of polynuclear isomers, the diiliculties ofseparation are particularly aggravated, especially since they usuallyform-mixed crystals and thus cannot be easily separated byrecrystallization. An example of such dcultly separable polynuclearisomers with which this invention is particularly concerned is theisomerc pair a-methyl naphthalene and -methyl naphthalene.

The problem of separating a-methyl naphthalene from -methyl naphthalenehas been quite thoroughly studied by a number of investigators. See forexample, Separation of the Aromatic Hydrocarbons and the Isolation ofn-Dodecane, Naphthalene, 1 Methyl Naphthalene, and 2- Methyl Naphthalenefrom the Kerosene Fraction of Petroleum by Mair and Streiif, ResearchPaper R. P. 1289, National Bureau of Standards, J. of Research, vol. 24,1940; and the articles by E. A. Coulson. appearing in the J. of theSociety of Chemical Industry: Preparation of aand -Methyl Naphthalenefrom Tar Oil Fractions, vol. 60, pp. 123 to 126 (1941); vol. 62,- pp.177 to to 179 (1943).

aand -Methyl naphthalene occur naturally in petroleum and coal-tar oilsand are inevitably found in admixture with one another. The isomers boilonly a few degrees apart, the a-isomer boiling at 244.8" C. and the,fi-isomer boiling at 241.1 C. at 760 mm. Hg. In addition to thisproximity of boiling points, the separation of these isomers is mademore diiTlcult by the fact that recrystallization alone cannot be usedsince the isomers form a eutectic consisting of about 82% of thea-isomer. By very careful fractionation in very eilcient distillationequipment followed by recrystallization at low temperature, it ispossible to obtain pure a-methyl naphthalene but the procedures involvedare tedious and expensive. The -isomer is somewhat easier to obtain in apure state. Since both isomers in their pure state have important usesas intermediates, and since a mixture of these isomers may be obtainedin commercial quantities in coal-tar oils, it is of importance toprovide a method for the separation of these isomers which is lesstedious and more economical.

In accordance with the present invention, a technique of azeotropicdistillation has been evolved which may be applied t0 the separation ofdiicultly separable organic isomers, particularly the polynuclear, andwhich has proven to be especially effective in the separation ofa-methyl naphthalene from -methyl naphthalene. It has been found thatthe separation of a-methyl naphthalene from -methyl naphthalene may beeconomically achieved by distilling a mixture containing these isomersin the presence of an entrainer which at a selected pressure forms adilute, low-boiling azeotrope with oneof the ismers and virtually noazeotrope with the other isomer. The low-boiling azeotrope of entrainerwith one of the isomers may be distilled from the mixture, leavingexcess entrainer and the 'other isomer in the still residue.

As entrainers for carrying out this process, a commercial undecanolhaving the formula 5-ethyl nonanol-2 and a boiling point of 225 C. at760 mm. Hg, and the compound 2-amino-3-methyl pyridine having a boilingpoint of 221 C. at 760 mm. Hg, have proven to be particularly suitable.For convenience, 5ethyl nonanol-2 will be hereinafter referred to asundecanol. Other entrainers than these may be used, however, which, at aselected pressure, have the property of forming a dilute azeotrope withone of the isomers but virtually no azeotrope with the other.

As a further important feature of the invention, it has been found thatafter the initial separation of the isomers the entrainer itself may beremoved from admixture with the isomers by one or more distillations atpressures different from that employed in the original distillation.

' More particularly, it has been found that the separation of afrom-methyl naphthalene may be achieved by adding to a mixture containingthese isomers an entrainer selected from the group consisting ofundecanol and 2-amino-3- methyl pyridine, distilling this mixture at asubatmospheric pressure selected so that the entrainer will form adilute azeotrope with -methyl naphthalene and virtually no azeotropewith amethyl naphthalene. The entrainer ,f3-methyl naphthalene azeotropeformed at the selected pressure boils appreciably below the boilingpoint of a-methyl naphthalene and may be fractionally distilledtherefrom with comparative ease. The distillation of the azeotrope maybe continued until all of the -methyl naphthalene has been removed asoverhead distillate, leaving only amethyl naphthalene and excessentrainer in the still residue.

In order that the invention might be better understood reference is nowmade to the drawings in which Figure 1 is a graph showing the variationAin composition of azeotropes of aand methyl naphthalene with undecanolat varying distillation temperatures corresponding to varyingdistillation pressures;

Figure 2 is a graph showing the Variation in composition of azeotropesof aand -methyl naphthalene with 2-amino-3-methyl pyridine at varyingdistillation temperatures corresponding to varying distillationpressures, and,

Figure 3 is a schematic outline of a continuous process for theseparation of aand -methyl naphthalene according to the method of theinvention.

Referring now to Figure 1, this graph illustrates the azeotropicbehavior of each of the isomers aand p-methyl naphthalene with undecanol(5-ethyl nonanol-2) as the distillation pressure changes. Curve I showsthe behavior of methyl naphthalene undeeanol azeotropes while curve 2shows the behavior of a-methyl naphthalene-undecanol azeotropes. Eachcurve was determined separately by distilling a sample of the pureisomer in an excess of undecanol at varying distillation pressures. Ateach particular pressure a small sample of distillate was collected at ahigh reux ratio and analyzed. Results of this procedure for both isomersis set forth in Table I below.

about 180 C.

40 becomes increasingly` larger.

'atentos 5 to form a very dilute azeotrope with undecanol.

It will be noted that as the distillation pressure decreases below 400mm. the mle percent of methyl naphthalene in the azeotrope increasesuntil at about mm. Hg an azeotrope contain- 10 ing over 50% -methylnaphthalene is obtained.

In the case of a-methyl naphthalene. however, virtually no azeotrope isformed until the distillation pressure is decreased to about 200 mm. Hgcorresponding to distillation temperature of With further decreases inpressure the concentration of a-methyl naphthalene in the undecanolazeotrope also increases until at 20 mm. Hg, corresponding to a.distillation temperature of 120 C., an azeotrope containing about 20 46%a-methyl naphthalene is obtained.

` Where both aand -methyl naphthalene form azeotropes with undecanol itwill be noted that the boiling points of these azeotropes at any givendistillation pressure are very close (see Table I).

Thus, if a mixture of undecanol and aand be impossible to separate themby fractional distillation. It can be seen however, that there is aconstant difference of about 6 to 8% in the composition of theazeotropes at any given dis` tillation pressure. In the range ofdistillation pressures were the azeotropes are rich in the methylnaphthalene isomers, this diiierence in composition is of littlesigniiicance. However, as the azeotropes become more dilute, the ratioof the -isomer tothe /a-isomer in the distillate For example, at 20 mm.Hg, corresponding to a distillation temperature of about 120 C.,azeotropes are formed rich in both aand ,B-methyl naphthalene, and thedistillate contains the and a-isomers in the ratio of about 1:2 to 1. At90 mm. Hg, corresponding to a distillation temperature of about 157 C.,the ratio of -isomer to a-isomer in the Table I a-isomer in undecanol-isomer in undecsnol Distil- Distil- Percent Distil- Dlstil- Per Centlation lation a lation lation 8 Pressure Temp. C Distillste PressureTemp. C Distillate 760 225 0 k7641 225 0 400 225 0 400 203 0. 5 300 1930. 6 300 193. 5 4. l 275 191 0. 7 250 188 6. 3 250 188. 5 0.8 m0 181. 58. 7 240 186. 5 i). 8 150 172. 5 16. 3 220 184 90 157 28. 0 200 179. 52. 4 50 140. 5 40. 3 175 176 4. 9 H) 120 54. 4 150 173 6.2 90 157.6 17.0143 28.8 19 121 45.9

For every distillation pressure there is, of course, a correspondingdistillation temperature and, for convenience, the composition of thedistillate has been plotted against the distillation temperature ratherthan the pressure. It will be noted that at atmospheric pressure, or 760mm. Hg, the distillation temperature in the case oi both isomers (seeTable I) is 225 C. cordistillate has increased to about 1.7 to 1.Finally, at about 250 mm. Hg an azeotrope containing about 6.3% of-methyl `naphthalene and less than 1% of a-methyl naphthalene is formedso that the ratio of ,8- to a-methyl naphthalene in the distillate isnow about 8 to 1.

The hydrocarbon-undecanol azeotrope' formed at any given pressure boilappreciably below the responding to the ,boiling point of undecanol,inboiling temperatures of the pure isomers at that pressure. Thus, bydistilling a. mixture of the isomers in the presence of undecanol at apressure at which undecanol forms a dilute azeotrope with -methylnaphthalene but virtually no azeotrope with a-methyl naphthalene, adistillate will be obtained many times richer in the -isomer while thestill residue rapidly becomes relatively richer in the a-isomer. Byusing a large amount of undecanol, this process may be continued untilall of the -methyl naphthalene has been relo moved as overheaddistillate, leaving only amethyl naphthalene and excess entrainer in thenaphthalene 2amino3methyl pyridine azeotropes while curve 2 shows thebehavior of 'imethyl naphthalene 2amino3methyl pyridine azeotropes.These curves were determined in the same manner as the curves in Figure1 by distilling a sample of the pure isomer in an excess of2-amino-3-methyl pyridine at varying distillation pressures, collectinga sample of distillate at a high reflux ratio and analyzing thedistillate for the aor -isomer. Results of this procedure for bothisomers is set forth in Table II below.

Table II a-isomer in -isomer in 2-amino-3-mcthyi pyridine 2-amono3methylpyridine Distil- Dlstii- Per Cent Distil- Distil- Per Cent lation lationa in lation lation in Pressure Temp. C Dstillate Pressure Temp. CDistillate 'i60 221 0 760 221 0 400 198 1.0 550 209 3.0 325 190 2.0 400196 6. 3 290 187 2.8 250 182 ll 250 177-181 3. 3 150 165 18. 6 150 1668. 1 90 151 23.0 90 159 10.0 50 137 25.0 50 136 19. 9 2l 116 28 115 26.2 20 115 33 19 114 3l 16 109 36 still residue. Small amounts of thea-isomer will usually distill over with the -isomer, but the ratio of toa in the distillate will be high.

It is, of course, possible to eiect a separation of the isomersby,distilling the mixture of isomers 3 with undecanol in a range ofpressures where Van azeotrope of the e-isomer with undecanol is formedcontaining an appreciable amount of the a-isomer. For example, rat adistillation pressure of about 130 mm. Hg corresponding approxi- 40 thatas the distillation pressure approaches that at which there is noazeotrope formed between undecanol and -methyl naphthalene, the methylnaphthalene undecanol azeotrope becomes progressively more dilute Iuntilat about 400 mm.

Hg an azeotrope containing only about 0.6% of 55 -methyl naphthalene isobtained. For economic reasons it is preferred not to operate in therange of pressure corresponding t0 extremely dilute methyl naphthaleneundecanol azeotro'pes, since this would require the evaporation ofexcessive' amounts of undecanol in order to achieve the removal ofappreciableamounts of the lf3-isomer. Preferably, the distillationpressure is selected so that the entrainer forms an azeotrope containingas large as possible a percentage of the isomer, while at the same timevirtually no azeotrope of the a-isomer with entrainer is formed. In thecase of undecanol, the preferred range of distillation pressures, basedon these considerations, is from about 200 to 300mm. Hg.

Referring now to Figure 2, this graph illustrates the azeotropicbehavior 3f each of the isomers aand -methyl naphthalene with 2-amino-2-methyl pyridine as the distillation pressure changes. Curve I showsthe behavior of -methyl As in Figure 1, the distillation temperaturerather than the pressure has been plotted against the composition of thedistillate. The behavior of the isomers in the presence of 2-amin-3-methyl pyridine is substantially the same as their behavior in the'presence of the undecanol entrainer. At atmospheric pressure neitherAoi? the isomers form an azeotrope with Z-amino-B- methyl pyridine. Atabout 550 mm. Hg corresponding to a distillation temperature of about209 C. the -isomer rst begins to form an azeotrope with 2-amino-3-methy1pyridine. the concentration of the -isomer in the azeotrope increasingas the pressure decreases. The a-isomer, on the other hand, formsvirtually no azeotrope until a distillation pressure of 400 mm. Hg(corresponding to a. distillation temperature of about 198 C.) isreached. With decreasing pressure the concentration of the a-isomer inthe azeotrope with Z-amino-S-methyl pyridine also increases, therealways being, however, a constant diierence of about 8% in thecomposition of the a-isomer azeotrope and the e-isomer azeotrope.

As is the case with undecanol, the azeotropes of the isomers with2-amino-3-methyl pyridine likewise boil close together, and the onlyeiective Way to separate the isomers is to distill them in the presenceof the entrainer at a pressure selected so that the entrainer forms adilute azeotrope with the lf3-isomer and virtually no azeotrope with thea-isomer. As in the case of undecanol, it is preferred not to operate inthe range of pressures corresponding to extremely dilute -methylnaphthalene 2-amino-3-methyl pyridine azeotropes since this wouldrequire the evaporation of excessive amounts of entrainer.

Using 2-amino-3-methy1 pyridine as the entrainer it is preferred tooperate in the range of from about 250 to 550 mm. Hg, since within thisrange the ratio of to a-methyl naphthalene in the distillate is high,while extremely dilute azeotropes of -methyl naphthalene with entrainerare avoided.

It is desired to emphasize the fact that the i 7 methodof the inventiondoes -not consist in the use of 'an' entrainer which will form anazeotrope with one isomer which at any given pressure, boils at asignificantly different temperature than the azeotrope formed with theother isomer under the same conditions. aand p-methyl naphthal'eneyandmany other isomers, are so structurally similar that the azeotropeswhich are formed with any given entrainer boil too close together toallow separation of the azeotrope's'by fractional distillation. This isillustrated for example by the azeotropes which aand -methyl naphthaleneform with undecanol and 2-amino-3-methyl pyridine. (See Tables I andII.) In the process of the invention, no

A ageehso's attempt is made to fractionate the azeotropesformed with anygiven entrainer, but rather an entrainer is chosen which will formazeotropes with isomers, the composition of the azeotropes varying withpressure in such a manner that within a selected range of pressures theentrainer will form a dilute azeotrope with one of the isomers andvirtually no azeotrope with the other. In distilling the mixture ofentrainer and isomers in the selected pressure range, both isomers mayform azeotropes to, some extent with the entrainer, but one of theseazeotropes will be so dilute that it is fair to say that virtually noazeotrope of this isomer is formed.

` In general, an azeotroping agent (that is, an entrainer), which willbe eiective in the process of the invention should have the followingcharacteristics:

1. It should have a boiling point from 10 to 50"v C. lower than theboiling point of the isomers to be separated. l l

2. It should be soluble in the isomers to be separated to avoid theformation of two liquid phases.

3. In admixture with the isomers to be separated it should form asolution which shows a substantial deviation from Raoults Law of IdealSolutions. In the case of predominantly hydrocarbon isomers such as aand`fi-methyl naphthalene, the most effective azeotroping agents are thosecontaining OH or NH groups.

'4. It is also essential that the distillation temperaturev at which theentrainer will form a dilute azeotrope with one of the isomers andvirtually, no azeotrope with the other should be below the decompositiontemperature of the isomers to be separated or that of the entrainer. Thedecomposition temperature of aand methyl naphthalene is in theneighborhood of 400 C.

In order to effect a complete separation of the isomers according to themethod of the invention, it will, in general, be necessary to use alarge excess of entrainer since the overhead distillate will contain alarge proportion, usually over 90%, of entrainer. For example, whendistilling a mixture of aand -methyl naphthalene in the presence ofundecanol under preferred conditions, the overhead distillate willcontain approximately 95% undecanol and 5% -methyl naphthalene. However,the amount of entrainer employed is not critical. So long as there isenough entrainer present to form a dilute azeotrope with one of theisomers at the selected pressure, separation according to the process ofthe invention will continue. All of the entrainer need not be addedinitially, but may be continuously or periodically added as distillationproceeds.

An important feature of the invention resides covered from admixturewith the separate isomers following the original distillation in whichthe isomers are separated from one another. In general, this isaccomplished by distilling the mixture of isomer and entrainer at apressure dlfferentfrorn that employed in the original distillation,taking-advantage of the fact that the composition of the azeotropeswhich the entrainer forms with each of the isomers varies withVdistillation pressure and that at some pressure no azeotrope'will format all.

For example, inthe case of the separation of and a-methyl naphthaleneusing an entrainer comprising undecanol or 2-amino-3-methyl pyridine,the -isomer will be recovered as a dilute solution in the entrainer. Asone alternative, this dilute solution could be distilled at atmosphericpressure at which no azeotrope is formed between the entrainer and the-isomer. However, since the entrainer boils at a lower temperature thanthe -isomer, this would require the distillation of very large amountsof entrainer to achieve the separation. Preferably, the dilute solutionof -isomer in the entrainer is redistilled at a pressure lower than thatused in the original distillation in order that an azeotrope may beformed rich in the -isomer. In this way, the relatively small amount of,tI-isomer in the mixture is rapidly removed as overhead distillate.Substantially pure undecanol is recovered as still residue and may bereturned to make up fresh feed for the original distillation. The fairlyconcentrated solution of -isomer in entrainer recovered as overhead fromthis redistillation is again distilled at a pressure higher than thatused in the original distillation whereby no azeotrope-is formed, andthe more volatile entrainer stripped away, leaving the -isomer asbottoms. i from -methyl naphthalene usingan undecanol entrainer, theredistillation of the dilute -isomer-undecanoi solution recovered asoverhead from the original distillation is preferably conducted at apressure below 90 mm. Hg. The concentrated -isonier-undecanol solutionrecovered as overhead distillate from this redistillation is thendistilled at a pressure over 460 mm. Hg, most conveniently atmospheric,:so that no azeotrope is formed between the -isomer and undecanol.-

The undecanol (boiling about 15 C. below the boiling temperature of-methyl naphthalene at 760 mm. Hg) is stripped away leaving the -isomerin the still.

Using 2-amino-3-methyl pyridine as the entrainer in the separation ofafrom -methyl naphthalene, the redistillation of the dilute isomer'2-amino-3-methyl pyridine solution from the original'distillation ispreferably conducted at a pressure below'i50 mm. Hg.Y The concentrated-isorner 2-amino-3-methyl pyridine solution recovered from thisredistillation is then distilled at' a pressure above 700 mm. Hg, mostconveniently' atmospheric pressure. vThe A2- amino-3-methylpyridine(boiling about 20 be- 10W the boiling temperature of -methyl naphthaleneat 760 mm. Hg) is stripped away leaving the -isomer in the still.

The same procedure as was used to separate the mixture of the-isomer`frorn the entrainer may be used to recover the a-isomer. If adilute solution of the a-isomer in the entrainer is recovered from theoriginal distillation, the solution may first be concentrated bydistilling at a pressure lower than that used in the original in themethod by which the entrainer may be redistillation in order to distiiloil an azetrope rich In the case of the separation of ain the a-isomer.Usually, however, the a-isomer will be recovered from the originaldistillation as a fairly concentrated solution in the entrainer sincemost of the entrainer is removed as an overhead distillate as anazeotrope with the -isomer. Thus, the a-isomer can usually be separatedfrom the entrainer by a single fractional distillation at a pressuregreater than that used in the original distillation. In the case ofundecanol and 2amino3methyl pyridine entrainers, this straightfractional distillation is most conveniently carried out at atmosphericpressure where the entrainer boils at a temperature from to below theboiling point of the a-isomer.

If desired, other means than distillation may be employed to separatethe isomers from the entrainer. For example, methods such as solventextraction and chemical precipitation may be employed in appropriatecases. For example, in the case of 2-amino-3-methyl pyridine, extractionwith aqueous RC1 or sulfuric acid, for example, may be used. The aminesalt can be recovered by evaporation to give a concentrated solution ofthe salt from which the free base can be recovered by neutralization.Where the entrainer is stable under the distillation conditionsnecessary to aiect separation, recovery of the entrainer from admixturewith the isomers is preferably eiected by the distillation technique setout above.

Reference is now made to Figure 3 which schematically illustrates acontinuous process for the separation of a-methyl naphthalene from-methyl naphthalene according to the method of the invention. A mixtureof the isomers to which has been added a large excess of entrainer iscontinuously fed to vdistilling column 3 Awhich is operated at apressure selected so that the entrainer will form a dilute azeotropewith -isomer but virtually no azeotrope with the a-isomer. In the caseof undecanol and 2amino3methyl pyridine entrainer this column isoperated at a subatmospheric pressure. Column 3 is equipped with asuillcient number of theoretical plates so that the dilute low-boilingazeotrope of the entrainer with the -isomer is continuously removed asan overhead fraction by line 4 and the higher boiling materialscomprising a nonazeotrophic mixture of u-methyl naphthalene andentrainer collect at the bottom. By properly adjusting the conditions inthe column according to methods well known in the art, the residuecollecting at the bottom is obtained virtually free of the -isomer andcomprises a relatively concentrated solution of the a-isomer in theentrainer, since most of the entrainer goes off in the overhead as anazeotrope with the -isomer. This relatively concentrated solutioncontaining the a-isomer is conducted to column 6 by line 5 andredistilled at a pressure diierent from that used in the originaldistallation, remote from the pressure at which azeotropes of thea-isomer with the entrainer are inclined to form. In the case ofundecanol and 2-amino-3-methyl pyridine entrainers, this seconddistillation is most conveniently conducted at atmospheric pressure.

` From this second distillation, the entrainer is removed as overheaddistillate by line 1 vand may y be returned to make up new feed forcolumn 3.

The a-isomer is removed from the bottom of column 6 by line 8 and may befurther purified by conventional methods. Further purication, however,is not usually necessary since purities up to 99% this point.

The overhead distillate from column 3. which comprises a dilute solutionof the -isomer in the entrainer, which is azeotrophic at the pressureprevailing in column 3, is conducted by line 4 to column 9. Column 9 ismaintained ata pressure below that prevailing in column 3 in order thatthe -isomer form a more concen trated azeotrope with the entrainer.Thus, for example, where the overhead distillate from col- Iumn 3contains 5% o1.' the -isomer, by operating column 9 at a pressuresubstantially lower than the pressure employed in column 3. the overheaddistillate removed from column 9 may comprise an azeotrope of the'entrainerwith -isomer containing more than 50% of the -isomer. In thismanner the -isomer may be removed from the bulk of the entrainer bydistilling only a relatively small amount of the dilute solution removedas overhead distillate from column 3. The entrainer, thus stripped ofthe -isomer may be removed from the bottom of column 9 and returned tomake up additional feed for column 3.

The relatively concentrated solution of the -isomer in entrainer removedas overhead distillate from column 9, is conducted by line lll to columnIl operated at a pressure at which the -isomer forms no azeotrope withthe entrainer. In the case of undecanol and 2-amino-3-methyl pyridineentrainers column Il is most conveniently operated at atmosphericpressure. The' entrainer is removed as ov'er' head distillate by line I2and may be returned to make up more feed for column 3. The -isomer,substantially free Aof entrainer is removed as still residue by line i3.'Ihe -isome'r will usually be contaminated by small amounts of thea-isomer which distilled off with the -isomer in the originaldistillation. Ordinarily, the a-isomer will be present in amounts lessthan 20% and a high percentage of the -isomer can be recovered from thismixture by recrysof the a-isomer may be obtained at tallization. Themother liquors from the recrystallization, relatively depleted in the-isomer. may be returned to column 3 for re- Example 1 A charge of about52 volumes of a-methyl naphthalene, 50 Volumes of -methyl naphthaleneand about 300 volumes of undecanol were distilled in a column havingabout 20 theoretical' plates under the prevailing distillationconditions, at a pressure of 260 mm. Hg. During thedistillationadditional quantities of undecanol, totaling in all about 2000 volumeswere periodically added. The distillation temperature ranged between 186to 190 C., or about 10 to 15 below the boiling points of the pureisomers at thisv pressure. 'I'he distillation was continued untilsubstantially all the -isomer was removed from the still, as indicatedby a change in the refractive index of the overhead distillate.

'I'he still residue contained only the a-isomer and undecanol. Thismixture was then distilled at atmospheric pressure (736 mm. Hg) in acolumn having about 20 theoretical plates under the conditions ofdistillation. The distillation temperature was 225 C. About 310 volumesof the original 52 volumes of the a-isomer were recovered in a purity ofover 99% without any further purification.

The overhead distillate from the original distillation, consisting of asolution containing about 94% undecanol, 5% -methyl naphthalene, and 1a-methyl naphthalene was distilled at a pressure of about 20 mm. Hg in acolumn operating at an eiliciency of about 20 theoretical plates. Thestill head temperature was 120 C. A distillate was recovered containingabout 50% oi undecanol, 40% of the -isomer, and 10% of the a-isomer. Thebulk of the undecanol was recovered substantially pure as still residue.The concentrated solution thus obtained was redistilled at atmosphericpressure and the remaining undecanol stripped off, leaving a mixturecontaining about 80% of the ,o8-isomer and 20% of the a-isomer.Substantially all of the original 50 volumes of the .-isomer werepresent in this mixture, and most of the 1L-isomer not recovered asstill residue in the original distillation was present in this mixture.

Example 2 A charge consisting of about 49 volumes of the a-isomer and 42volumes of the 1B-isomer and about 400 volumes 2-amino-3-methy1 pyridinewas distilled in a column operating at .an efciency of 20 theoreticalplates, at a pressure of 325 mm. and at a still head temperature of 192C. This distillation was continued until substantially all the -isomerwas removed from the still residue as indicated by a change in therefractive index of the overhead mixture.

To recover the a-methyl naphthalene, the still residue, consisting of amixture of this isomer with 2-amino-3-methyl pyridine, was acidiiiedwith aqueous hydrochloric acid followed by extraction with benezene torecover the a-isomer from the amine salt. The a-isomer was recovered inthe purity over 97%.

The overhead distillate-from the original distillation, consisting of asolution containing about 90% 2amino3methyl pyridine, 8% of the -isomer,and 2% of the a-isomer, was treated in a manner similar to thatdescribed in Example 1. The dilute solution was first concentrated bydistillation at a low pressure, and the concentrated solution thusobtained redistilled to remove the remaining 2-amino-3-methyl pyridine.A mixture of aand ,i1-methyl naphthalene was thus obtained containingabout 80 of the -isomer and 20% of the ci-isomer.

Although this invention has been described particularly in reference tothe separation of aand -rnethyl naphthalene, the same technique ofazeotroplc distillation described in reference to separation of thesetwo isomers may also be applied in the separation of otherclose-boiling, difcultly separable isomers.

The pure a.- and -methyl naphthalene isomers obtainable according to theprocess of the invention have several important commercial uses. Forexample, the -isomer maybe simply transformed `into2-methyl-1,4-naphthoquinone, a pharmaceutical having antihemorrhagicactivity, for example, by direct oxidation with chromic anhydride inacetic acid as a solvent. Similarly, the -isomer may serve as anintermediate in the preparation of vitamin K. The a-isomer may bereadily converted into a-naphthyl acetic acid, an important plant auxinby oxidation of the methyl group. The eute'etic mixture of aand-naphthalene, containing about 82% of the a-isomer, may be prepared bydistillation according to the method of the invention to give a fuelmixture having a desirable pour point characteristics for extreme lowtemperatures.

It is to be understood that the above description and examples areintended merely to be illustrative of the invention, and that theinvention is not to be limited thereby, nor in any way except by thescope of the appended claims.

l. A method for separating a-methyl naphthalene from -methyl naphthalenecomprising the steps of adding an entrainer comprising 2-amino-3-methylpyridine to a mixture containing these isomers, and distilling theresultant mixture at a subatmospheric pressure selected so that said2-amino-3-methyl pyridine forms an azeotrope at least with -methylnaphthalene. Y

2. A method for separating a-methyl naphthalene from -methyl naphthalenecomprising the steps of adding an entrainer comprising Z-amino-E-methylpyridine to a mixture containing these isomers, and distilling theresultant mixture at a reduced pressure between 250 and 550 mm. Hg,whereby 2-amino-'3-methyl pyridine forms a dilute azeotrope with -methylnaphthalene but virtually no azeotrope with a-methyl naphthalene.

3. A method for separating a-methyl naph-l thalene from -methylnaphthalene comprising the steps of adding an entrainer comprising2-amino-3-methyl pyridine to a mixture containing these isomers, anddistilling the resulting mixture at a reduced pressure between 250 and550 mm. Hg, whereby 2-ainino-3-methyl pyridine forms a dilute azeotropewith -methyl naphthalene but virtually no azeotrope with a-methylnaphthalene, removing said dilute azeotrope as overhead distillate untilthe s'till residue is virtually depleted of -methyl naphthalene,concentrating said dilute azeotrope by redistillation at a pressurebelow mm. Hg whereby a -methyl naphthalene-rich azeotrope is formed,redistilling said -methyl naphthalene-rich azeotrope at a pressure above'700 mm. Hg to recover p-methyl naphthalene virtually free from saidentrainer.

4. A method for separating ii-methyl naphl thalene from -methylnaphthalene comprising the steps of adding to a mixture containing theseisomers an entrainer comprising Z-amino- S-methyl pyridine, distillingthe resultant mix- Ature at a subatmospheric pressure selected so thatsaid entrainer forms a dilute azeotrope with -methyl naphthalene butvirtually no azeotrope with a-methyl naphthalene, removing an overheaddistillate of the dilute azeotrope of entrainer with -methyl naphthaleneuntil the still residue is virtually depleted of -methyl naphthalene,redistilling said dilute azeotrope of -methyl naphthalene with entrainerat a pressure different from that employed in the original distillationto recover said -methyl naphthalene virtually free from said entrainer,and redistilling said still residue at a pressure different from thatemployed in the original distillation to recover said -methylnaphthalene virtually free from said entrainer.

5. A method for separating a-methyl naphavances thalene from -methylnaphthalene comprising the steps of adding to a mixture containing theseisomers an entrainer comprising Z-amino- S-methyl pyridine, distillingthe resultant mixture at a subatmospheric pressure selected so that saidentrainer forms a dilute azeotrope with -methyl naphthalene, butvirtually no azeotrope with a-methyl naphthalene, removing an overheaddistillate of the dilute azeotrope of entrainer with -methyl naphthalenewhereby the stili residue becomes relatively enriched in a-methylnaphthalene, redistilling said dilute azeotrope of entrainer and -methylnaphthalene at a subatmospheric pressure lower than the pressureemployed in the original distillation whereby an 15 14 azeotrope ofentrainer with -methyl naphthalene is formed relatively richer in-methyl naphthalene, removing said -methyl naphthaiene-rich azeotrope asoverhead distillate while recovering said entrainer virtually free fromlf2-methyl naphthalene as still residue, and redistilling said -methylnaphthalene-rich azeotrope at a pressure greater than that employed inthe original distillation to recover -methyl 10 naphthalene virtuallyfree from said entrainer.

. JULIAN FELDMAN. MILTON ORCHIN.

No references cited.

1. A METHOD FOR SEPARATING A-METHYL NAPHTHALENE FROM B-METHYLNAPHTHALENE COMPRISING THE STEPS OF ADDING AN ENTRAINER COMPRISING2-AMINO-3-METHYL PYRIDINE TO A MIXTURE CONTAINING THESE ISOMERS, ANDDISTILLING THE RESULTANT MIXTURE AT A SUBATMOSPHERIC PRESSURE SELECTEDSO THAT SAID 2-AMINO-3-METHYL PYRIDINE FORMS AN AZEOTROPE AT LEAST WITHA-METHYL NAPHTHALENE.